Sleep disordered breathing which results in the diagnosis of Obstructive Sleep Apnea (“OSA”) occurs as a result of a partial or complete collapse of the upper airway during sleep. Snoring is the first indication of an airway susceptible to collapse and can lead to inspiratory flow limitation. Greater obstruction resulting in a partial collapse of the airway causes hypopneas and recognizable changes in tidal volume. Full collapse results in a cessation in breathing, events commonly referred to as apneas. The apnea/hypopnea index (AHI) is the measure used to define OSA severity and is based on the total number of sleep disordered breathing events per hour of sleep.
When a patient with OSA is in the supine position, gravity increases the susceptibility of the airway to partial or full collapse during sleep. The most frequently cited effect of gravity on the soft tissue of the pharynx is tendency of the tongue to fall back against the palate causing the narrowing of an already compromised airway. A susceptible airway, by way of example, may result in loud snoring in the supine position and limited or no snoring the non-supine position. A more compromised airway may exhibit loud snoring in the non-supine position and repeated hypopneas (partial collapse) or apneas (full collapse) in the supine position. This pattern is typically associated with patients with ‘positional’ sleep disordered breathing. In patients with severely compromised airways, known as ‘non-positional’ OSA, the pharynx may partially collapse during non-supine sleep and fully collapses in the supine position. The influence of gravity during supine sleep contributes to a reduction in lung volume and oxygen stores and contributes to increased levels of oxygen desaturation during obstructive breathing.
Evidence suggest that patients with positional and non-positional OSA form two distinct but overlapping etiologies in which airway length and craniofacial features influence genioglossal responsiveness to negative pressure pulses in the lateral position. Estimate of the prevalence of positional OSA (i.e., the supine AHI is at least two times greater than the non-supine AHI) among all those diagnosed with OSA range from 55 to 65%), and after excluding those who sleep almost exclusively on their back (e.g., >95% of the night), over 50% of patients diagnosed with sleep could reduce their AHI by at least 50% and/or into a normal range by avoiding sleep in the supine position. Studies have shown that position therapy can contribute to a significant drop in blood pressure in patients with Obstructive Sleep Apnea (OSA) because supine sleep increases the severity of OSA. Position therapy can be combined with other therapies to enhance outcomes in the treatment of sleep disordered breathing. Several investigators have demonstrated nasal continuous positive airway pressure (CPAP) pressures can be reduced if patients sleep lateral instead of supine and increased CPAP compliance has been associated with lower pressures.
A plethora of shirts, vests, belts, pillows and other inventions have attempted to address the need for positional therapy to reduce the severity of snoring or sleep apnea by using mechanical means that essentially makes it uncomfortable for a user to sleep supine. Some examples of these devices include a knapsack stuffed with Styrofoam to provide a bulky alternative to tennis balls, which makes it impossible to sleep supine. At least one study has demonstrated that this type of position restriction provides limited to no clinical efficacy due to non-compliance. The greatest limitation of these approaches is that the therapy is initiated prior to the patient falling asleep. As shown with CPAP therapy, patients are much more tolerant of therapy if it is initiated after the patients have fallen asleep.
The number of electronic devices invented to limit supine sleep is substantially less. One device, described in U.S. Pat. No. 5,081,447, employs the use of two gravity position sensors and an audio alarm to trigger the user to change position. One of the limitations of this approach is a bed-partner of the user would also be awakened each time the alarm is triggered. An alternative approach, described in U.S. Pat. No. 5,381,801, limits supine sleep by applying electromechanical vibration using motors inserted into pockets of a belt worn by a user. Application of the tactile stimulus is dependent on the closing of an electronic switch within the pocket of the belt that is triggered by contact with the underlying surface of the sleeper.
Positional therapy holds the potential to provide important therapeutic benefit for a number of medical conditions. For example, over 63% of patients with acute ischemic stroke sleep the entire night in the supine position. Sleep in the supine position also increases the severity of Cheyne-Stokes i.e., respiration i.e., central sleep apnea. Avoiding supine sleep during the second and third trimesters of pregnancy would reduce pressure on a vena cava vein and improve blood flow to the fetus. An adjustment in the application of position feedback would assist patients recovering from hip surgery avoid sleep in the non-supine position. The measurement of and feedback related to the position of the elements of the body (e.g., arm, leg, hand, wrist, ankle, knee, etc.) could be useful in injury rehabilitation or in training or performance which requires the user to find or maintain a specific position/posture. Thus, the potential benefit of positional therapy is clear, but conventional systems and methods to affect or influence sleep position have been largely ineffective.